The present invention relates to a method of manufacturing a shadow mask type of cathode ray tube for color television and, more specifically, to a tube having colored optical filter elements on the inner surface of the tube faceplate.
In the manufacture of certain types of shadow mask cathode ray tubes for color television, it is desirous to incorporate a colored optical filter element between each phosphor segment or dot and the tube faceplate. These color filters are designed to transmit the desired portion of the wavelength spectrum emitted by the respective phosphor dot, e.g., red, green or blue, and absorb all other visible light, including that impinging from the ambient illumination. One method for obtaining these filter elements is to use organo-metallic resinate materials, such as are available from Englehard Industries as lusters, applied in thin films and patterned in the appropriate manner to give the correct filter elements under each phosphor. These resinate films when fired at or above 430.degree. C are converted to a thin hard layer showing good adherence and intense colors on transmission.
In a conventional method for providing these filters, the hole patterns which must be present in each filter layer on the tube faceplate may be introduced using traditional photolithographic techniques. A layer of photoresist, such as polyvinyl alcohol (PVA) is applied to the inner surface of the faceplate, exposed through the shadow mask and developed to leave resist at the hole sites. The resinate film is laid over this and fired at approximately 430.degree. C to form the filter. Due to poor adhesion in the areas formerly occupied by the photoresist which is now decomposed, the film may be removed by abrasive action, leaving holes in the remaining film. Each layer is treated in the same manner.
While this method has been generally satisfactory, it has several disadvantages. First, the method has many steps including resist application, exposure, and development for each film. Also, for three layers, three high temperature firings are required. Further, the removal of fired film from the hole areas requires an operation which may damage the remaining film and leave random holes incompletely cleared.